Fine.
Then prove for me using scripture alone that there is one God in Three Persons, each Person wholly and entirely God, all co-equal, co-eternal, and possessing the divine nature totally unto Himself, the Godhead having but one divine intellect and one divine will.
This modern orthodox Christian understanding of the Trinity comes from the doctrinal definitions of the RCC, not the clear sense of sola scriptura, yet you accept it and embrace it.
Without the Tradition of the Church of Rome handing down this orthodox teaching of Christianity, you would have no clear understanding of this doctrine, and the LDS understanding would be just as valid as your own.
Why is the LDS understanding wrong?
Not because it is refuted by scripture. Frankly it is not clearly refuted by scripture.
It is wrong because it is refuted by the orthodox Tradition of the RCC.